Neurological impairment, such as spinal cord injury (SCI), can occur in people of any age, and is often caused by injuries sustained in accidents associated with motor vehicles, firearms, sports injuries, and the like. Many of the individuals who sustain such injuries are young male adults between the ages of 16 and 30 who, up to the point of the accident, have lead active and healthy lives.
In the USA, the prevalence of neurological impairment resulting from SCI is estimated at between 712 and 906 per million with the incidence of SCI being calculated at between 30 and 40 per million. It is widely recognised that SCI has a large impact on society in general and is a sudden and irreversible change to an individual's quality of life.
In order to define SCI, it should be understood that an SCI is a traumatic lesion to the spinal cord and the associated nerves. Thirty-one spinal nerves originate from the spinal cord and can be grouped as follows: 8 cervical (C1 to C8), 12 thoracic (T1 to T12), 5 lumbar (L1 to L5), 5 Sacral (S1 to S5) and 1 coccygeal. An injury to the spinal cord can result in varying degrees of impairment depending on where and to what extent the spinal cord is injured. In general, the higher up on the spinal cord the injury, the more severe the resulting impairment.
People suffering from a SCI are essentially categorised into two main groups: tetraplegics and paraplegics.
Tetraplegics are individuals who have sustained injury to one of the eight cervical segments of the spinal cord, C1 to C8. Such an injury results in impaired use of the arms and hands as well as the legs. A person who has suffered such an injury generally experiences significant loss of sensation and volitional body movement as well as the loss of volitional bladder and bowel control. Many tetraplegics may also have loss of psychogenic and impaired reflex erections.
Paraplegics are individuals who have sustained an injury at the thoracic level, T1 to T12. These individuals usually have sensation and volitional control over their upper limbs, but have lost sensation and control of their lower limbs and bladder and bowel control, as well as erection problems in males.
Due to SCI individuals being unable to control bladder function, individuals must regularly self cathertise. This procedure is problematic, especially for females, and can result in an increase in the incidence of urinary tract infections. Still further, persons suffering from SCI must often undertake lengthy bowel evacuation procedures using, for instance, digital evacuation. SCI patients are also prone to secondary medical problems, such as pressure sores, osteoporosis, muscular atrophy in the lower limbs, muscle spasticity, deep vein thrombosis, cardiovascular disease and depression. Pressure sores are caused by the occlusion of blood flow during sitting and lying and are a major health problem which may require surgery to repair and months of rehabilitation including requiring the patient to remain lying on their abdomen for an extended period of time.
Therefore, whilst restoration of bladder and bowel control is a primary need of SCI individuals, reduced incidence of pressure sores is also highly needed. This, together with the ability to exercise and stand and step, are functions that would greatly improve the quality of life of SCI individuals.
It is therefore evident that a large proportion of the population who have a SCI would benefit from a device that would be able to assist in, at least, the partial restoration of such lost functionality, in particular bowel and bladder function, erectile function, the reduction in the incidence of pressure sores and the provision of exercise and upright mobility. Various systems have been proposed by numerous organisations to deal with one or other of the functions that have been lost to SCI individuals.
There have been systems designed for bladder control via an implantable device that have met with variable success with the majority of such devices requiring invasive surgical procedures such as posterior sacral rhizotomies and sacral laminectomies. The “Vocare” device manufactured by Finetech Medical Limited (UK) requires a posterior sacral rhizotomy and a laminectomy, in order to achieve a non-reflexive bladder with adequate capacity, and also requires a sacral laminectomy to access the anterior sacral roots to enable the cuff type electrodes to be fitted. This surgical procedure eliminates reflex erection in male recipients and it is considered that an individual who receives a rhizotomy but does not use the device would be expected to have reduced bowel activity.
There have been a number of systems proposed to assist in limb control, particularly lower limb control. The majority of such systems, such as the “Parastep” system from Sigmedics (Wheeling, Ill., USA), rely upon surface stimulation techniques that use external electrodes placed on the user's limbs to stimulate the muscles via an electric charge through the skin. Such systems are limited with regard to the functionality they can restore to the limbs due to the non-specific way that stimulation is applied. Implantable systems have also been proposed to control limb movements directly. These systems use a plurality of electrodes to stimulate targeted muscle groups, either in the lower limbs or in the arms/hands.
It will be appreciated that SCI results in loss of control over multiple physiological systems, and implants to date have only been developed to restore individual functions. A need therefore exists to provide a generic implantable stimulator capable of restoring multiple functions to an SCI individual and the stimulator being controllable by various functions or modes that are matched to an individual patient's requirements. There is also a need to provide a generic FES implant that requires less invasive surgical procedures, and only one source of control rather than multiple sources.